1. Field of the Invention
This invention relates to surgical devices generally and more specifically to orthopedic implants for stabilizing fractured bones, especially a human femur.
2. Description of the Related Art
Intramedullary rods (sometimes called “nails”), usually of a steel or titanium alloy, are used in orthopedic surgery to aid in the fixation of long bone fractures. The originator of the Intramedullary rod implant was a German surgeon called Kuntscher; for this reason the original implant was sometimes called a “Kuntscher nail.” Eventually Kuntscher's nailing technique, became a common orthopedic procedure, especially for fractured femurs or Tibias.
Modern orthopedic practice is slightly different from that used by Kuntscher, and is referred to as “Closed nailing.” To fix a fracture with an intramedullary rod, the fracture is first reduced. Then a small hole is made usually at the top of the bone (antegrade placement). A reamer is typically used to prepare the intramedullary canal to snugly receive a rod-like implant. Usually a thin guide wire is slid down inside the bone, across the fracture and into the next fragment. A long rod is then inserted longitudinally and generally axially into the intramedullary canal, the rod spanning the unstable, fractured area. Often, interlocking screws are inserted generally diametrically through holes drilled in the intact sections of the bone, both above and below the fracture. The interlocking screws pass through the bone and through transverse holes in the intra-medullary rod, thereby transfixing the bone to the inserted rod and longitudinally and torsionally stabilizing the fracture.
Depending on the innate stability of the fracture, the screws may be essentially static and provide rigid, inflexible fixation of the bone without significant compression. If the fracture is longitudinally stable, the interlocking screws can be threaded through elongated holes or slots in the intra-medullary rod, thus allowing the fractured bone ends to be pressed together somewhat. This method allows some limited compression, due to gravity or (in some cases) muscular contraction; but compression only occurs sporadically, if weight bearing can be tolerated.
Research has shown that a more sustained, controlled, and dynamic compression across a fracture is desirable to promote rapid healing. Furthermore, it is known that in many fractures, bone resorption typically precedes mending. A rigid intra-medullary rod cannot accept any degree of bony contraction.